1. Field of the Invention
This invention relates to paste-form detergents for use in institutional laundries and to a process for their production.
2. Discussion of Related Art
Detergents used in the home are adapted to domestic requirements. Thus, they are normally powders or are sufficiently liquid to lend themselves to problem-free pouring and dosing. Since liquid detergents are also expected to be stable in storage over relatively broad temperature ranges, organic solvents and/or hydrotropes are often added to them although they do not themselves make any contribution to the washing/cleaning result and, for this reason, are not wanted. One way of avoiding possible dosing problems with insufficiently liquid detergents is proposed in European patent application EP 253 151 A2. This document describes liquid and, in some cases, highly viscous detergents based on nonionic and anionic surfactants which contain polyethylene glycol as hydrotrope and which do not have to be dosed in liquid form by the user, but instead are packed in portions in bags of water-soluble material, for example polyvinyl alcohol.
The paste-form detergent described in European patent EP 295 525 B1 consists of a liquid phase of nonionic surfactant which is liquid at temperatures below 10.degree. C. and--dispersed therein--a solid phase with a certain particle size consisting of washing alkalis, sequestering agents and optionally anionic surfactants. The surfactants or surfactant mixtures used must have a pour point (solidification point) below 5.degree. C. to avoid solidification of the paste at low transportation and storage temperatures. This detergent paste is intended for institutional laundries and has such good flow properties that it can be pumped through a suction line by a conventional delivery pump. However, it has been found that pastes of the type in question are not always able satisfactorily to guarantee the homogeneity of their ingredients during the production process and often tend to separate, even in storage. This separation involves not only the separation of solid from liquid ingredients, but also phase separation of the liquid ingredients.
Another paste-form detergent which contains as nonionic surfactant from 40 to 70% by weight of ethoxylated C.sub.10-20 fatty alcohol--liquid at room temperature--with an average degree of ethoxylation of 1 to 8, 20 to 50% by weight of ethoxylated and propoxylated C.sub.10-20 fatty alcohols--liquid at room temperature--with an average degree of ethoxylation of 2 to 8 and an average degree of propoxylation of 1 to 6 and 1 to 10% by weight of soap is described in International patent application WO 95/09229. This paste-form detergent is so pseudoplastic that it does not flow under the effect of gravity at room temperature, but assumes a distinctly lower viscosity on shearing and then flows under the effect of gravity. This paste-form detergent is preferably dosed by shearing to reduce its viscosity and then dosing the flowable product using feed pumps.
In automatic batch washing machines in particular, detergents often lead to foaming problems which can have particularly unpleasant effects at the rinsing and pressing stages. The formation of foams at these stages would appear to be attributable to the presence of surfactants, more especially nonionic surfactants, which have accumulated on the washed laundry and which pass from the final rinse to the rinsing and pressing stages under high mechanical stressing. Besides the operational problems caused by excessive foaming, irritation of the skin through the presence of relatively large quantities of surfactant on the washed laundry cannot be completely ruled out.
In addition, demands to stop using detergent ingredients which have been found to lack sufficient biodegradability have also recently been raised in institutional laundries. These demands are particularly difficult to satisfy because the cleaning performance of the detergents used has to meet very much stricter requirements by comparison with the conditions prevailing in domestic washing. This applies in particular to the surface-active ingredients which make a key contribution to the cleaning result and among which synthetic anionic surfactants, particularly of the sulfonated alkyl benzene type, play a prominent role in this regard.
Accordingly, the problem addressed by the present invention was to provide a paste-form detergent for use in institutional laundries which would show a reduced tendency to foam at the rinsing and pressing stage and which would lead to smaller quantities of surfactant on the washed laundry and would also combine high stability in storage with high cleaning performance although it would be at least largely free from the synthetic anionic surfactants of the alkyl benzenesulfonate type normally required for this purpose.
Surprisingly, these problems have largely been solved by optimizing the nonionic surfactant component and by using long-chain alcohols and/or long-chain alkyl ethers.